The instant invention relates to a plastic ball socket for a grease lubricated ball joint which socket is formed of two sections, an inner hemispherical interior cup and an outer cup, such as those disclosed in U.S. Pat. No. 3,647,249 and British Pat. No. 629,906. Such ball joints find much use in the automotive industry as steering tie rod joints and wheel suspension joints. It is common to find such ball joints having a synthetic material socket having a closed sealing sack and a permanent grease packing. Such joints have the advantage of not requiring regular servicing but have a main drawback in that during use, the wear and tear on the joint results in abrasive pieces being mixed with the grease. This results in a reduction in the lubricating properties of the grease which in turn accelerates the wear and tear on the parts and soon the joint becomes unusable.
In known ball sockets, slots or grooves are cut into the socket as channels for lubricants for the joint. The upper edges of these grease slots or grooves, although they are usually rounded, in practice often act to strip the lubrication from the spherical surface of the ball which the ball joint socket is supporting. This contributes further to the wear and tear of the ball joint unit during use and therefore decreases the useful life of the ball joint.
Multi-level or composite sliding bearings are known, for instance the Mackensen bearing, wherein grease is carried in a greasing slot or groove in the form of an elongated pocket formed by elastic deformation of a respective thin walled bushing. Such a device requires a peripheral velocity for the bearings in order to form the furrows or pockets which act as the grease slots or grooves. As there is usually no appreciable circumferential velocity associated with ball joints of the type intended for use with the instant invention, the required peripheral velocity to permit lubrication using a Mackensen type bearing, is absent.